Congestive heart failure (CHF) is a leading cause of death in the United States. CHF occurs when the heart is unable to adequately supply enough blood to maintain a healthy physiological state. CHF can be treated by drug therapy, or by an implantable medical device (IMD) such as for providing cardiac pacing therapies, including resynchronization therapy (CRT) to correct cardiac dyssynchrony within a ventricle or between ventricles.
The IMD can chronically stimulate excitable tissues or organs, such as a heart, to treat abnormal cardiac rhythms or to help improve cardiac performance in a patient with CHF. Such ambulatory medical devices can have at least first and second electrodes that can be positioned within the heart or on a surface of the heart for contacting the cardiac tissue. The electrodes can be electrically coupled to an electronics unit such as a pulse generator, such as via a lead, and can be used to deliver one or more electrostimulations to the heart, such as to restore or to improve the normal heart function.
The IMD can also sense cardiac signals using the electrodes on one or more leads. The cardiac signals can be sensed as a voltage signal across two sensing electrodes. Depending on the location of the sensing electrodes, the IMD can sense various cardiac electrical events such as depolarization of a heart chamber, such as an atrium or a ventricle. Proper sensing of cardiac electrical events can provide useful diagnostic information including progression of a cardiac disease, such as worsening of CHF, and be used to determine cardiac therapies such as cardiac pacing including the CRT therapies.